1. Field of the Invention
The present invention relates to a device for coupling an agricultural implement to an agricultural tractor.
2. Description of the Related Art
In general, a link is provided at the rear of an agricultural tractor. A device for coupling an agricultural implement (hereinafter referred to as “coupling device”) is attached at the rear end of the link. When an agricultural implement is coupled to an agricultural tractor, first, a coupling ball provided in the front portion of the implement is accommodated in a hook portion provided in the coupling device of the agricultural tractor. Next, the coupling ball is locked with a stopper of the coupling device so as not to be escaped from the hook portion of the coupling device. When the coupling is to be released, first, the operator pulls a control lever of the coupling device so as to slide the stopper to the coupling-ball-releasing position, and the stopper is held in that position. Next, the coupling ball is removed from the hook portion of the coupling device to release the coupling.
European Patent No. 0937592 discloses a conventional coupling hook comprising a hook body, a blocking device, a control lever, resilient means and a pivoting lever. The hook body includes a hook-shaped portion housing a coupling ball. The blocking device is housed in a cavity of the main body. The blocking device can slide through a first opening (slit) so as to block and release the coupling ball. The control lever is housed in the cavity of the body. The upper portion of the control lever protrudes from a second opening. The control lever slides the blocking device so as to block and release the coupling ball. The resilient means are for holding the blocking device in the blocking position. The pivoting lever is rotatably coupled to the hook body, the blocking device and the control lever. In addition, the pivoting lever is coupled to the resilient means. The control lever includes a clamping tooth. The clamping tooth is provided in the middle in the vertical direction of the rear part of the control lever. The hook body includes a correspondingly shaped portion to the clamping tooth. The correspondingly shaped portion is provided on the outside of the hook body, in front of the first opening. When the coupling ball is released, the control lever is pulled upward so as to slide the blocking device into the cavity. Next, the control lever is turned backward so that the clamping tooth of the control lever engages with the correspondingly shaped portion provided on the body of the hook. Thus, the control lever is fixed to the body of the hook, and the coupling ball is released.
In addition, Japanese Patent No. 2601409 discloses a coupling hook comprising a hook body, a locking pawl and a closing spring. The hook body includes a bearing recess for accommodating a coupling ball. The locking pawl is provided in the hook body and blocks the coupling ball. The closing spring urges the locking pawl toward the locking position. When the coupling ball is released from the coupling hook, first, an opening lever is pulled so as to bring a supporting face into contact with a round bearing surface. The supporting face is a groove provided in the opening lever. The bearing face is provided in the boundary region of a through-aperture of the hook body. Next, the opening lever pivots around the round bearing surface so as to slide the blocking device to a releasing position where the locking pawl releases the bearing ball. Next, a second fixing stop is brought into contact with an arresting stop. The second fixing stop is provided on the opposite side of the opening lever from the supporting face. The arresting stop is provided on a region at the outside of the hook body across the opening from the bearing face. At the same time, the opening lever is slid toward the bearing recess. Following the supporting face of the opening lever, a first fixing stop is retracted so as to rest on the bearing face. The opening lever is thus fixed to the hook body.
The coupling hook of the above-mentioned European Patent includes a blocking device, a control lever, a lever element and resilient means on top of the hook body. Therefore, there are a large number of parts and the cost can be high. In addition, for the release of the engaged coupling ball, the control lever needs to be pulled, to be turned backward while retaining the pulling state, and to be engaged with the hook body. Thus, the operation from the driver's seat, which is located diagonally in front of the coupling hook, becomes complicated.
In the coupling hook of the above-mentioned Japanese Patent No. 2601409, for release of the coupling ball is released, a plurality of steps are necessary. That is to say, (1) pulling the opening lever upward so as to slide the blocking device to the releasing position where the locking pawl releases the bearing ball, (2) having the opening lever pivot around the bearing surface provided in the through-aperture of the hook body from the state that the opening lever is pulled, and (3) after having the opening lever pivot, sliding the opening lever toward the bearing recess so as to bring the first and second fixing stops of the opening lever into contact with the arresting stop and the bearing face provided in the through-aperture, respectively. Therefore, operation for releasing the coupling is complicated.